1. Field of the Invention
The present invention relates to a method of processing vegetable products to make foodstuffs which simulate animal meat in appearance and texture and flavor when appropriately flavored. More particularly, the method of the invention relies on a modified extrusion cooking-texturization technique for ma king vegetable protein products such as soybean foodstuffs, optionally with various additives which have a fiber-like texture resembling choice cuts of cooked meat.
2. Description of the Background
Cooked meat is the heat-denatured, intact striated muscle of animal, fowl or aquatic species. The essential unit of muscle tissue is a long multinucleate fiber consisting of a cluster of myofibrils which hold a solution of sarcoplasm between them. The fiber is covered by a very thin membrane, the sarcolemma, to which connective tissue is bound on the outside. In turn, the fibers are arranged in parallel bundles to form muscles, which are then formed into a sheath. The muscles are attached to a bone, tendon or other rigid structures in pairs of a major and a minor muscle. When the major muscle contracts the minor muscle relaxes. The minor muscle then contracts returning a relaxed major muscle to its original position, thus permitting the chest muscles and diaphragm to work the lungs, and the legs, wings, fins, or tails to move. This parallel but covered structure permits the muscles, and the fibers within the muscles, to slip by each other while contracting or relaxing.
During cooking, a muscle loses its elasticity due both to denaturation of myofibril proteins and a loss of its ability to hold the sarcoplasmic solution. However, cooked meat retains its basic structure formed of many parallel fibers, each with its individual cover. When meat is chopped, ground, or otherwise reduced to discrete shreds and the mass is reshaped as in making hamburger patties, the shortened muscle shreds are placed in random order but each shred retains its fiber-like substructure. This structure provides a resilient feeling in the mouth when the food is chewed.
Early attempts by the food industry to simulate the fibrous structure of meat, with, e.g., soy protein, developed around a simplified model of natural meat. The model comprises a system involving the manufacture of fibers or sheets of texturized soy protein held together by suitable binders such as edible albumin. When the multilayers are cut into elongated strips, they simulate, in visual appearance, fibrous strands of meat. The technology then developed to extrusion of spongy masses of protein with elongated collapsed air or steam cells, whose ruptured walls give the appearance of aligned fibers.
U.S. Pat. No. 3,950,564 to Puski et al. discloses a modified extrusion method for processing soy protein flour into elongated strands which visually resemble fibrous masses of meat. The emphasis in the Puski et al. patent is primarily directed at the improvement of processed vegetable protein foods to make them visually simulate meat. The single extrusion method of the Puski et al. patent, however, provides a product having a substantially limited texture of meat. Nor do Puski et al texturize by oil- or fat-coating the fibers between two extrusion steps.
U.S. Pat. No. 3,852,483 to Oborsh et al discloses and claims a process of manufacturing a starch-based product that mixes a farinaceous material, a proteinaceous material and water with a glyceryl monostearate starch conditioner in specified proportions, so that the latter will react with starch and bind water thereto. The mixture is then extruded once at high temperature and pressure, and propylene glycol added to the surface of the thus formed particles for preservation purposes prior to fat-coating and heating.
Currently available methods for making vegetable protein meat extenders utilize primarily dehulled, defatted soy flour or a soy protein concentrate. U.S. Pat. Nos. 3,537,859 and 4,031,267 disclose methods of extruding aqueous mixtures of defatted soy flour to produce expanded, soy-based meat substitutes. The emphasis in those methods is on replacing natural meat with a protein-rich, nutritious constituent. The resulting products are soft and porous and the emphasis is on nutrition and not on consistency and texture.
Thus, there is always a need for improved nutritious, protein-rich foodstuffs that resemble the appearance, texture, and taste of meat and can be prepared at a lower cost.